"Uptown without being Uptown"

East 52nd definitely starts off with some New York City Posh. Cartier is right on the corner of 5th and the French restaurant, La Grenouille is directly across the street. The Ferragamo store nextdoor to the restaurant is the former site of Madame Restell's mansion. She was the leading abortion provider until the 1870's and she committed suicide when she was arrested. Pretty crazy story for such a stuffy area. There are a lot of big business buildings on this street like banks, Harper Collins publishing and The Omni Hotel. It's all pretty boring stuff but the site of the Omni is where the millionaire William Rice lived. His valet and lawyer tried to doctor a fake will leaving his money to them and they murdered him in his home. The fraud was found and the fortune went to the founding of Rice University. I kinda wish they would have just converted the actual mansion into a hotel rather than demolish it but I guess that's a little maudlin for most peoples' tastes.
There are a lot of hotels that line 52nd around Madison and Park -- some of the more notable ones being The Four Seasons and The Gladstone. The subway vent where Marilyn Monroe's dress flew up in the Seven Year Itch is on the corner of 52nd and Lex.
The corner of 52nd and 3rd was the site of a boardinghouse where Albert Fish was finally arrested. I didn't really know much about the guy or why that was significant when someone pointed it out. I did some research on the guy and he may have been one of the most depraved killers who ever lived. So, I wouldn't set foot in that building just in case there was any bad energy transfer. Yikes. If you're into serial killers, though, then this is a significant corner.
Conversely, two of the cities nicest apartment buildings are at 52nd and 1st: The Campanile and River House. Noel Coward, Greta Garbo, Cornelius Vanderbilt and Marshall Field are included in the residents lists of these buildings.
East 52nd is crazy because it goes from high end to halfway house back to super high end. It's really boring, but for wealthy people with kids in the city, I can see how the sleepier part of town is more desirable.

"Stuck in the Middle"

Not quite the posh tree-lined enclave of the Upper East Side, not quite the buzzing commercial area of midtown, the East 50's are one of the rare parts of New York City to lack a distinct neighborhood character. Around 5th Avenue, the area is gorgeous and elegant - here is the shopping capital of the world, where Bergdorf's and Bendel's are populated by an international jet-setting (and jet-shopping) elite. But head further east and the landscape changes, transforming into a largely sedate area filled with office buildings and their attendant amenities (plenty of Starbucks and sandwich delis). By the time you reach the East River, however, you've found your way to another up-and-coming neighborhood: the stunning river-views in these modern developments have attracted a number of young professionals drawn by the low prices and picturesque panoramas, and the far East 50's have a decidedly "young" vibe. Hit up some up-and-coming-bars like the River Club, Mimi's, Travis, and the perennially popular Le Perigourd, popular with the uber-posh old money Sutton Place set located just a few blocks to the north.